Game engine for Return to Castle Wolfenstein

Free agile arena shooter

Source port for Build engine games

Shoot and survive

The Free and Fast Arena Shooter

Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy

dhewm 3 is a Doom 3 GPL source port

Tank digging battle game

Fast paced, first person strategy game

Open Source voxel shooter

FPS aim trainer

Yamagi Quake II is an alternative client for id Software's Quake II

A modernization effort of DOOM-3-BFG

Leading the way in newschool multiplayer Doom online

Classic arena first person shooter

Epic story-driven FPS running on the Build Engine

First-person shooter with cooperative in-game map editing

Game engine for Classic Doom

A Zandronum 3.0 fork with improved netcode, configurable movement and many small tweaks

First-person shooter game

Top-down shooter action RPG

Free fast paced arena shooter

EDuke32 is an awesome, free homebrew game engine

Open source first person shooter

a modern QuakeWorld client focused on competitive online play

Open source first person shooter

A modern cross‑platform port of “STAR WARS™: Dark Forces” with mod support

A Quake mod based on the retro shooter SPRAWL

The orb ponderer's arena first-person shooter

Modern cross-platform port of the Descent engine